The present invention relates to a turbomachine blade, for example a compressor blade for a gas turbine engine and in particular to a fan blade for a gas turbine engine.
Conventional narrow chord fan blades for gas turbine engines comprise solid metal.
One conventional wide chord fan blade comprises a concave metal wall portion, a convex metal wall portion and a honeycomb between the two metal wall portions. This wide chord fan blade is produced by hot forming the wall portions into concave and convex shapes respectively, placing the honeycomb between the metal wall portions and brazing, or activated diffusion bonding, the metal wall portions together around the honeycomb. The interior of the fan blade is evacuated.
Another conventional wide chord fan blade comprises a concave metal wall portion, a convex metal wall portion and metal walls extending between the two wall portions. This wide chord fan blade is produced by placing a metal sheet between two tapered metal sheets and diffusion bonding the sheets together at predetermined positions to form an integral structure. Then inert gas is supplied into the interior of the integral structure to hot form the integral structure into a die to produce the concave and convex walls and the walls extending between the concave and convex walls. The interior of the fan blade is evacuated.
A disadvantage of a wide chord fan blade is that it is not as stiff as a narrow chord fan blade. The reduced stiffness results in an increased risk of stalled flutter within the operating range of the gas turbine engine and an increased susceptibility to other forms of vibration. A further disadvantage of the wide chord fan blade is that it is very expensive and time consuming to produce.
Accordingly the present invention seeks to provide a novel turbomachine blade which reduces, preferably overcomes, the above mentioned problems.
Accordingly the present invention provides a turbomachine blade comprising a root portion and an aerofoil portion, the aerofoil portion having a leading edge, a trailing edge, a concave metal wall portion extending from the leading edge to the trailing edge and a convex metal wall portion extending from the leading edge to the trailing edge, the concave metal wall portion and the convex metal wall portion forming a continuous integral metal wall, the aerofoil portion having a hollow interior defined by at least one internal surface, the hollow interior of the aerofoil portion being at least partially filled with a vibration damping material, the vibration damping material being bonded to the at least one internal surface and the vibration damping material comprising a material having viscoelasticity.
Viscoelasticity is a property of a solid or liquid which when deformed exhibits both viscous and elastic behaviour through the simultaneous dissipation and storage of mechanical energy.
Preferably the whole of the interior of the aerofoil portion is filled with vibration damping material.
Preferably the vibration damping material comprises a polymer. The vibration damping material may comprise a structural epoxy resin. The vibration damping material may contain glass microspheres, polymer microspheres or a mixture of glass microspheres and polymer microspheres. The vibration damping material may be formed by mixing an amine terminated polymer and bisphenol a-epichlorohydrin epoxy resin.
Preferably the turbomachine blade is a compressor blade or a fan blade.
The present invention also provides method of manufacturing a turbomachine blade from at least two metal workpieces comprising the steps of:
(a) forming at least two metal workpieces,
(b) applying stop off material to a predetermined area of a surface of at least one of the at least two metal workpieces,
(c) arranging the workpieces in a stack such that the stop off material is between the at least two metal workpieces,
(d) heating and applying pressure across the thickness of the stack to diffusion bond the at least two workpieces together in areas other than the preselected area to form an integral structure,
(e) heating and internally pressurising the interior of the integral structure to hot form the at least two metal workpieces into an aerofoil shape to form a turbomachine blade having a hollow interior defined by at least one internal surface,
(f) cleaning the internal surface of the hollow interior of the turbomachine blade,
(g) supplying a vibration damping material into the hollow interior of the turbomachine blade and bonding the vibration damping material to the internal surface, the vibration damping material comprising a material having viscoelasticity, and
(h) sealing the hollow interior of the turbomachine blade.
Preferably each of the at least two sheets has at least one flat surface and the flat surfaces of the at least two sheets are arranged to abut each other.
Preferably the at least two sheets increase in thickness longitudinally from a first end to a second end.
Preferably the second ends of each of the at least two sheets are arranged adjacent to each other to form the root of the turbomachine blade.
Preferably step (d) comprises heating to a temperature greater then 850xc2x0 C. and applying a pressure greater than 20xc3x97105 Nmxe2x88x922.
Preferably step (d) comprises heating to a between 900xc2x0 C. and 950xc2x0 C. and applying a pressure between 20xc3x97105 Nmxe2x88x922 and 30xc3x97105 Nm2.
Preferably step (e) comprises heating to a temperature between 700xc2x0 C. and 850xc2x0 C.
Alternatively step (e) comprises heating to a temperature between 850xc2x0 C. and 950xc2x0 C.
Preferably the at least two metal workpieces comprise titanium or a titanium alloy.
Preferably the vibration damping material comprises a polymer. The vibration damping material may comprise a structural epoxy resin. The vibration damping material may contain glass microspheres, polymer microspheres or a mixture of glass microspheres and polymer microspheres. The vibration damping material may be formed by mixing an amine terminated polymer and bisphenol a-epichlorohydrin epoxy resin.
Preferably step (f) comprises sequentially flushing the hollow interior of the turbomachine blade with nitric acid, a neutraliser and water to remove the stop off material from the internal surfaces of the hollow interior of the turbomachine blade.